The chemical element content of Red Blood Cells (bulk: C, Fe, S, P and ionic: K, Na, Cl, Mg) will be measured by automated electron probe analysis, counting all these elements by the same method in the same individual RBC in large number. The mounting procedure will avoid ionic translocation by spraying the RBC. Best method will be analysis of the cells maintained in a frozen hydrated state prepared either in bulk using lapidary technique under liquid nitrogen or thin using cryomicrotomy. An electron probe with two special cold stages for bulk or thin sample will be used. These states are cooled by circulation of liquid nitrogen. By inducing a reversible increase in monovalent cations permeability with nystatin treatment, it will be possible to obtain cells with standardized Na, K and Cl concentration. Such cells will provide calibration curves to calculate Na, K and Cl concentration in individual normal cells. Absolute method of quantitation will provide the concentration of the elements measured in individual cells. Multiple correlation will be studied between all the chemical elements counted. Histograms of elemental content will be compared between elements for the same population of cells. For a given element, histograms will be systematically studied in human RBC in function of the age and sex of the donor and in function of the age of the RBC. These parameters will be studied in pathological RBC and in RBC from different species. The technique developed will be extended to other isolated cell systems and histochemical reactions.